fix: emit valid XPath node test for ID elements in full-path mode

Address review feedback: In full-path XPath generation, elements with
IDs were producing bare predicates like `[@id='x']` which creates
invalid XPath steps like `//body/[@id='main']`. Now emits `*[@id='x']`
for full-path mode (e.g. `//body/*[@id='main']/*[@id='target']`).

Short-path XPath mode unchanged — still uses `//*[@id='x']` prefix.

Also added XPath evaluation assertion to the regression test to verify
the generated selector actually selects the correct element.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

scrapling/core/mixins.py

@@ -26,7 +26,12 @@ class SelectorsGeneration:
             if target.parent:
                 if target.attrib.get("id"):
                     # id is enough
-                    part = f"#{target.attrib['id']}" if css else f"[@id='{target.attrib['id']}']"
+                    if css:
+                        part = f"#{target.attrib['id']}"
+                    elif full_path:
+                        part = f"*[@id='{target.attrib['id']}']"
+                    else:
+                        part = f"[@id='{target.attrib['id']}']"
                     selectorPath.append(part)
                     if not full_path:
                         return " > ".join(reversed(selectorPath)) if css else "//*" + "/".join(reversed(selectorPath))